This invention relates to a unique battery jar cover which has been designed to be welded onto a battery jar by means of automatic heat sealing equipment. Specifically, this invention concerns the manufacturing of a composite structure which comprises a storage battery which includes an outer jar or container of suitable non-current conducting and acid resisting material in which conventional battery elements and terminal posts have been previously placed which is closed by the cover described herein. Further, the welding of this cover to battery jars can be accomplished in a more efficient and effective manner by improved processing techniques made possible by this cover structure.
It is, of course, desirable when preparing this composite battery structure that the cover be effectively sealed around its periphery to the top of the battery jar so that notwithstanding in service conditions, including both high and low temperatures, vibrations, or other work environment conditions, that the seal between the cover and the rim of the battery jar remain intact. Thus, what is desired is a seal that is a substantially permanent, hermetic seal that is acid proof and that can resist at least the above service conditions, while at the same time providing strength at the joint.
Is also desirable, to the extent possible, to automate the process of welding battery jar covers onto battery jars. One difficulty in this regard, is created by the fact that the battery jars have electrodes in place so that their terminal posts extend upwardly beyond the plane established by the upper rim of the battery. Thus, in the past, it has been necessary to manually place covers on battery jars followed by the manual application, of some type of sealing composition or joint compound to fill and the joint area between the cover and the battery jar's upper rim. Examples of such joints can be found in Dusenburg U.S. Pat. No. 557,779 and Badt U.S. Pat. No. 576,936.
Alternatively, and more recently, the joint between battery covers and battery jars has involved an open upwardly directed groove between the upper surface of the cover and the rim area of the jar that would allow the insertion of thermosetting material between the cover and the battery jar. The thermosetting material could be a resin or cement compound which would thereafter be cured or permanently set without pressure or accelerators when baked for a relatively long period at about 200.degree. F. Burns et al U.S. Pat. No. 2,603,671 is exemplary of this latter technique.
Still more recently, battery covers have been glued or sealed onto battery jars by means of epoxy adhesives or by ultrasonic welding. In many cases the ultrasonic process is not capable of producing a hermetically sealed container at the point of the weld especially where there are thick or complicated tongue and groove type joints since such structures are believed difficult to penetrate with the ultrasonic waves. Thus, acid leaks can occur at points along the weld or from poorly secured areas where the thickness to be penetrated was too great to provide a completely solid weld. Ultrasonic welding requires the material be relatively stiff and works best where the ultrasonic electrodes can be on opposite sides of the work piece. Accordingly use along corner structures, as would be required when welding battery covers onto battery jars, provides a difficult set of conditions which would have to be overcome in order to produce a good weld. Likewise, glueing procedures do not always result in a continuous hermetically sealed joint around the entire structure and in some cases requires the cover to be turned upside down so that glue can be placed in a groove into which the battery jar rim is ultimately placed after the whole jar has been inverted. Since the lid element is within the battery jar at this point and it may weigh many pounds, it is a difficult process to turn the entire jar assembly upside down in order to correctly position it on the top. Exemplary patents are Thornblad et al U.S. Pat. No. 3,449,170 and Jammet U.S. Pat. No. 3,627,586.
There have been a relatively wide variety of cover shapes. Some have mitered joints such as in Jammet, U.S. Pat. No. 3,627,586, or tongue and groove joints as in Burns et al U.S. Pat. No. 2,603,671 while in others grooves have been provided either in the cover itself as in Thornblad et al U.S. Pat. No. 3,449,170 or in the upper rim of the jar as in Dusenburg U.S. Pat. No. 557,779 or Badt U.S. Pat. No. 576,936.
In addition, covers are known in the art that have a raised, flat rim area extending away from the bottom side of the cover and extending around the periphery thereof. The width of the raised area is as wide as the thickness of the side wall of the battery jar so that the two surfaces define between them a horizontal welding surface.
Covers are also known that employ a continuous flange which depends from the bottom surface of the cover with the flange being recessed inwardly from the edge just so as to define a horizontal bonding surface from the flange to the edge along the bottom of the cover. In this arrangement there is relatively tight engagement between the outer surface of the flange and the inner wall of the battery jar. In some cases, these tops have been glued with epoxy adhesive to the battery jar and in other cases the covers have been held, manually, in a slightly raised condition and a thermosetting or other sealing material is inserted within the opening provided between the cover and the rim of the battery jar and that material is thereafter allowed to set in place. Because the flange is pressed against the interior side wall of the battery jar none of the sealing material can flow downwardly between the two faces so that sealing will rarely occur therebetween.
It is believed that when heat welding thermoplastic materials that at the area of the joint only about 95% of the original tensile strength and a much lower percentage of the original elongation of the thermoplastic material can be regained upon resolidification so that if the joint itself is only as thick as the elements on either side thereof the joint area will be relatively weaker and be more likely to break than the wall areas on either side. With regard to bonding thermoplastic materials reference is made to Welding of Plastics, Neumann and Bockhoff, Reinhold Publishing Co., 1959. The manner and method of making battery jars is disclosed in a copending application, U.S. patent application Ser. No. 862,560, filed on Dec. 20, 1977 earlier U.S. Pat. Nos. 3,993,507 and 4,118,265 the subject matter of which is incorporated herein by reference thereto. Joints that are no thicker than the walls on either side are weaker than such side walls and such a structure does not have great impact strength in the horizontal direction. Accordingly, horizontal shear forces that can result if the side wall of the battery jar adjacent the joint were hit or struck in some way there can damage such joints perhaps resulting in a separation between the cover and the battery jar at the point the force is applied.
Further, in many bonding techniques currently in use the cover must be lifted entirely off of the battery jar and away from the terminals so that a heating platen, provided with a central cut out portion capable of fitting over the terminals, can be bought in and lowered into position to heat the joint even. After melting the heater is removed and the cover is finally brought back in place where it is held until the jar area is cooled. The time lag in such procedures is relatively long and some cooling and oxidizing of the plastic can occur, which is undesirable.